“Roundworms” or “nematodes” (phylum Nematoda) are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Over 80,000 species have been described, of which over 15,000 are parasitic. It has been estimated that the total number of described and undescribed roundworms might be more than 500,000. Unlike cnidarians or flatworms, roundworms have a digestive system that is like a tube at both ends.
Nematodes have successfully adapted to nearly every ecological niche from marine to fresh water, from the polar regions to the tropics, as well as the highest to the lowest of elevations. They are ubiquitous in freshwater, marine, and terrestrial environments, where they often outnumber other animals in both individual and species counts, and are found in locations as diverse as Antarctica and oceanic trenches. They represent, for example, 90% of all life on the seafloor of the Earth. The many parasitic forms include pathogens in most plants and animals (including humans.) Depending on the species, a nematode may be beneficial or detrimental to plant health.
From an agricultural perspective, there are two categories of nematodes: predatory ones, which will kill garden pests like cutworms; and pest nematodes, like the root-knot nematode, which attack plants.
Predatory nematodes can be purchased as an organic form of pest control.
Rotations of plants with nematode-resistant species or varieties are one means of managing parasitic nematode infestations. For example, marigolds, grown over one or more seasons (the effective is cumulative), can be used to control nematodes. Another is treatment with natural antagonists such as the fungus Gliocladium roseum. Chitosan is a natural biocontrol that elicits plant defense responses to destroy parasitic cyst nematodes on roots of soybean, corn, sugar beets, potatoes and tomatoes without harming beneficial nematodes in the soil.
Nematicides are agents that may be used to kill or control nematodes. One common nematicide is obtained from neem cake, the residue obtained after cold-pressing the fruit and kernels of the neem tree. Known by several names in the world, the tree has been cultivated in India since ancient times and is now widely distributed throughout the world. Nematophagous fungi, a type of carnivorous fungi, can be also be useful in controlling nematodes, Paecilomyces is one example.
Prior to 1985, the persistent halocarbon DBCP was a widely used nematicide and soil fumigant. However, it was banned from use after being linked to sterility among male farm workers. Aside from chemicals, soil steaming can be used to kill nematodes. Super-heated steam may be induced into the soil which causes almost all organic material to deteriorate.
In spite of attempts to control nematodes and other soil borne diseases, there remains a significant unmet need for effective nematicidal and soil borne disease controlling compositions to control and prevent unwanted nematode pests and other soil borne diseases.
Irrigation methods are becoming more efficient, such as the use of dripper irrigation, but this in itself leads to new problems such as deep percolation.
Soil life forms include fungi, nematodes, algae, and insects.
Nematodes control other nematodes, insects and other organisms. Many nematodes are harmless to the plant, but some are plant parasites.